1. Field of the Invention
The present invention relates to a pinion slip-off preventive structure of a starting apparatus for preventing a pinion, pressed toward a ring gear side by means of an elastic member, from slipping off a pinion shaft.
2. Description of the Related Art
FIG. 5 is a partial cross sectional view of a known starting apparatus for an internal combustion engine.
The starting apparatus illustrated includes an electric motor (not shown) having a first gear 2 mounted on a shaft 1, a second gear 3 in meshing engagement with the first gear 2, a drive shaft 4 splined to the second gear 3, an electromagnetic member (not shown) having a plunger (not shown) driven to reciprocate by means of an electromagnetic coil (not shown), a shift lever 5 engaged at one end thereof with the plunger so that it is caused to rotate like a seesaw through a reciprocating movement of the plunger, a one-way clutch 6 being in abutting engagement with the other end of the shift lever 5 so that it is driven to reciprocate in an axial direction under the action of a pressing force of the shift lever 5, a pinion shaft 7 extending from the one-way clutch 6 in an axial direction thereof, a pinion 9 splined to a spline portion 8 formed at one end of the pinion shaft 7 and meshed with a ring gear or flywheel starter gear (not shown) of an internal combustion engine, an elastic member 10 for pressing the pinion 9, mounted on the one end of the pinion shaft 7, toward a ring gear side, and a pinion slip-off preventive structure 11 for preventing the pinion 9, pressed in a direction toward the ring gear by means of the elastic member 10, from coming or slipping off the pinion shaft 7.
The one-way clutch 6 includes a drive member 13 splined to a helical spline 12 formed on the drive shaft 4 and acting as a clutch outer member, and a driven member 15 formed integral with the pinion shaft 7 and acting as a clutch inner member.
As illustrated in FIG. 6, the pinion slip-off preventive structure 11 comprises a snap ring 17 of a C-shaped configuration fitted in a groove 16 formed on the spline portion 8 in a circumferential direction thereof, and a stopper 18 being in abutting engagement with an end face of the pinion 9 and having an engagement portion 19 engaging with the C-shaped snap ring 17.
With the starting apparatus for an internal combustion engine as constructed above, when an unillustrated starting switch is turned on, the unillustrated electromagnetic coil in the electromagnetic portion is supplied with electric power and energized to move the unillustrated plunger in one direction, whereby the shift lever 5 is caused to rotate in a seesaw-like manner to urge the one-way clutch 6 to the right in FIG. 5. As a result, the one-way clutch 6 is driven to move together with the pinion 9 while being rotated in accordance with a lead angle of the helical spline 12, so that the pinion 9 is placed into meshing engagement with the unillustrated ring gear. Thereafter, the unillustrated electric motor is energized to rotate its rotation shaft 1. The rotation force of the rotation shaft 1 of the motor is transmitted to the driven member 15 through the intermediary of the drive shaft 4, the drive member 13 and a roller 14, whereby the pinion shaft 7 and the pinion 9 made integral with the driven member 15 are caused to rotate together with the driven member 15. The rotation of the pinion 9 causes the ring gear meshed with the pinion 9 to rotate, thus starting the internal combustion engine.
Here, note that when the pinion 9 is not able to mesh with the ring gear, the elastic member 10 is thereafter compressed by the movement of the pinion shaft 7, and at the same time, the pinion 9 is forced to rotate under the action of the lead angle of the helical spline 12 so that it is placed into meshing engagement with the ring gear.
After the internal combustion engine has been started, the power supply to the electromagnetic coil is stopped so that the plunger is returned to its original position, which was taken prior to the energization of the electromagnetic coil, under the action of the elastic force of the elastic member in the electromagnetic portion. However, since the shift lever 5 is rotated in a seesaw-like manner in accordance with the movement of the plunger, the one-way clutch 6 is pushed to return to the original position as taken before the starting of the internal combustion engine. Thus, the meshing engagement between the pinion 9 and the ring gear is released.
Also, an unillustrated motor energizing switch is turned off to stop the power supply to the electric motor. As a result, the rotation of the drive shaft 4 stops and the starting apparatus of the internal combustion engine is returned to the original state as taken prior to engine starting.
With the pinion slip-off preventive structure 11 of the starting apparatus as described above, the snap ring 17 is fitted in the groove 16 formed on the spline portion 8, and the elastic load applied to the snap ring 17 from the elastic member 10 is supported by the spline portion 8, as illustrated in FIG. 7. Therefore, there arises a problem that a pressure-receiving area of the snap ring 17 becomes small, and hence the snap ring 17 is subjected to an accordingly increased bearing and is liable to be worn out and damaged, thus giving rise a fear that the pinion 9 may slip off the pinion shaft 7.